The lysine-sensitive aspartokinase (AKIII) of E. coli appears to undergo rapid, specific proteolysis when cell growth ceases under a variety of conditions. We are trying to find out what specific sequence of events leads to the disappearance of AKIII. Under some circumstances the enzyme is labeled with P32 and we suspect that adenylylation or other nucleotede incorporation may be the trigger for proteolysis. We are precipitaing the enzyme by specific antisera to measure P32 incorporation at different stages of cell culture and under various conditions that inhibit proteolysis to try obtain highly labeled enzyme. This material will be examined for enzymic activity, physical properties and susceptibility to proteolysis.